This invention relates to a novel screw and matching driver bit. In particular, it relates to a screw having an undercut slot in its head and to a bit that engages the slot.
Power screwdrivers are now used more and more, especially when a large number of screws must be fastened. Power screwdrivers can produce greater torque than can a human. But if the driver is not stopped immediately when the bottom of the head of the screw hits the surface into which the screw is being driven, both the slot in the screw and the bit can be stripped, destroying the bit and making it difficult to remove the screw. It is not easy to stop the driver just when the head of the screw contacts the surface, so stripped screws and ruined bits are common. This is especially true of Phillips screwdrivers (X-shaped slots) and square drives (where the slot is a square well) because the bit engages the slot so close to the center of the head of the screw that there is very little turning leverage.
In addition, the torque of the driver tends to force the bit out of the slot, so that the operator must apply considerable pressure to the driver to keep the bit in the slot.
U.S. Pat. No. 5,868,049 shows a screw having an undercut slot in the head and an hourglass-shaped driver bit that engages the slot. However, the slot and driver bit are of a complex design which would be costly to produce.
I have invented a screw and driver bit that overcome some of the problems with prior screws and driver bits. The undercut slot in the head of the screw of this invention is a simple, straightforward shape. It is similar to the slot of a regular screwdriver and the screws should cost about as much to make as regular screws. The driver bit, too, is a simple shape, similar to a regular screwdriver, except for a foot at each end.
Unlike some prior screw heads and driver bits, the driver bit of this invention applies torque at or near the periphery of the screw head, not near the center of the screw head. As a result, the turning leverage is greater and there is far less tendency to chew up the screw head and the bit.
The slot in the head of the screw is wide enough for the bit to enter it from directly overhead, without any twisting motions by the operator. When the bit is engaged, it resists removal until the bit stops turning, whether the screw is being driven in or is being removed.
In addition, unlike the design in U.S. Pat. No. 5,868,049, the sides of the slot are not vertical, but are at an angle, with the widest portion of the slot farthest from the head of the screw. As a result, the torque of the driver forces the bit down into the slot, further ensuring that the bit does not disengage from the head while the screw is being driven.